It is well known that aircraft braking systems typically comprise a plurality of discs alternately connected to the wheel and axle of the aircraft. The urging together of this cylindrical stack of discs achieves the braking function. In doing so, however, a great deal of heat is generated, particularly in the carbon discs presently used in aircraft. Because of this intense heat, there is a need to shield the wheel, brake components, landing gear components, and other structure of the aircraft to prevent damage, fatigue and the like. Heat shields have been provided to either encase the brake disc stack or to selectively shield aircraft components from the stack. The implementation of such shields has met with a reasonable degree of success.
Known prior art wheel heat shields are typically of metal fabrication, configured into cylindrical or tubular members to be received over the brake disc stack. Typically, the heat shields are multi-layered, comprising between two and four concentrically spaced cylindrical elements. Generally, the greater the number of layers or cylindrical elements comprising the shield, the better the insulation and shielding provided by the unit. Indeed, insulation materials are sometimes substituted for the inner metal layers. However, as the number of layers of cylindrical members increases, the temperature gradient through the thickness of the shield increases. It is elementary that the inner layers, closest to the brake disc stack, are subjected to a greater temperature increase than the other layers of the shield. Accordingly, expansion of the inner layers exceeds that of the outer layers and, with such layers being fixedly interconnected, cracking, warping, and distortion of the heat shield results, giving rise to safety considerations, reduced efficiency, and increased maintenance costs. In other words, since the temperature gradient through the thickness of the heat shield varies from the inner surface to the outer surface of the shield, the thermal forces on the heat shield also vary through its thickness, resulting in the problems aforesaid. Most particularly, problems arise at the points of interconnection of the various layers of the heat shield due to relative expansion caused by heat transfer and dissipation. Since the prior art has taught that the heat shield should be fixedly secured together and also fixedly secured to the wheels, there has been provided no means for accommodating relative movement between the layers or to accommodate expansion and contraction of the heat shield as a whole to eliminate the distortion and fatigue inherent in such rigid systems.
There is a need in the art for a heat shield which allows for relative movement between the various layers of the heat shield itself, while also accommodating lateral expansion and contraction of the heat shield as a unit, without introducing failure or fatigue.